Exhaust structure of film-forming apparatus, film-forming apparatus, and method for processing exhaust gas

ABSTRACT

A film-forming apparatus  100  includes a processing chamber  11 , and TiCl 4  gas and NH 3  gas are supplied into the processing chamber  11  for forming a TiN film on a substrate W in the processing chamber  11  by CVD. The processing chamber  11  has a gas exhaust system  300 . The gas exhaust system  300  includes a gas exhaust pipe  51  for exhausting the exhaust gas in the processing chamber  11 , a trap mechanism  54  provided to the gas exhaust pipe  51  for trapping a by-product in the exhaust gas, and a heated reaction gas supply mechanism  60  for supplying a heated reaction gas into the exhaust gas. The heated reaction gas is adapted to react with a component in the exhaust gas to produce a by-product. Specifically, NH 3  gas is supplied by the heated reaction gas supply mechanism  60  as the heated reaction gas, and NH 4 Cl is produced as the by-product.

FIELD OF THE INVENTION

The present invention relates to a gas exhaust system of a film-formingapparatus for forming a predetermined film by CVD, a film-formingapparatus having the gas exhaust system, and a method for processing anexhaust gas.

BACKGROUND OF THE INVENTION

In manufacturing semiconductor devices, various processes, such as filmformation, quality modification, oxidation/diffusion, etching and thelike, are performed on a semiconductor wafer as a substrate to beprocessed.

For the film formation, there is widely used a CVD (Chemical VaporDeposition) method for forming a predetermined film through a chemicalreaction by introducing a predetermined processing gas into a chamberaccommodating a semiconductor wafer. In the CVD method, a film is formedby the reaction of the processing gas on the semiconductor wafer as asubstrate to be processed. At this time, however, only 10% of theprocessing gas contributes to the reaction, and most of the processinggas remains unreacted.

The unreacted processing gas reacts with a reaction gas in the chamberor in a gas exhaust pipe into which the reaction gas is introduced, toproduce a by-product. The by-product thus produced flows together with aby-product produced when forming a TiN film. When the by-products arecooled, a pipe is clogged or a vacuum pump is damaged. To that end, ingeneral, a trap mechanism for trapping a by-product is provided at thegas exhaust pipe extending from the chamber.

Although it is preferable that the by-product is trapped by the trapmechanism in the form of a compound that is easily trapped and has acomparatively stable structure, the by-product produced at a flow rateratio of each processing gas for film formation is not necessarilyturned into a desired compound. Therefore, Japanese Patent Laid-openPublication No. 2001-214272 discloses a technique for producing atrappable by-product by introducing directly into a trap mechanism orinto an upstream pipe a reaction gas that reacts with an impurity gasdischarged from the chamber.

In theory, a desired stable by-product that is easily trapped can beproduced by introducing a specific reaction gas. In practice, however,the reaction may proceed insufficiently, so that an unstable by-productor a by-product having an indefinite structure such as a complex or thelike may be produced. Accordingly, the trap mechanism needs to be scaledup due to hard to trap the by-product and, also, the trap mechanism maybe irregularly clogged due to an unreliable generation state (density orthe like) of a reaction product.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a gas exhaustsystem of a film-forming apparatus which is capable of stably trapping adesired high-density by-product, a film-forming apparatus having the gasexhaust system, and a method for processing an exhaust gas.

In accordance with an aspect of the invention, there is provided a gasexhaust system of a film-forming apparatus for forming a film by CVD ona substrate placed in a processing chamber by supplying a processing gasinto the processing chamber, the gas exhaust system of the film-formingapparatus including: a gas exhaust pipe connected to the processingchamber, for exhausting an exhaust gas in the processing chamber; a trapmechanism provided to the gas exhaust pipe, for trapping a by-product inthe exhaust gas; and a heated reaction gas supply mechanism forsupplying a heated reaction gas into the exhaust gas, the heatedreaction gas adapted to react with a component in the exhaust gas toproduce a by-product.

Preferably, a TiN film is formed by CVD on the substrate placed in theprocessing chamber by supplying TiCl₄ gas and NH₃ gas as the processinggas into the processing chamber and, at the same time, NH₄Cl is producedas a by-product by supplying NH₃ gas as the heated reaction gas from theheated reaction gas supply mechanism.

Preferably, the NH₃ gas as the heated reaction gas is supplied whilebeing heated at about 170° C. or higher.

Preferably, the heated reaction gas supply mechanism supplies the heatedreaction gas to an upstream side of the trap mechanism on the gasexhaust pipe via a pipe.

Preferably, the heated reaction gas supply mechanism supplies the heatedreaction gas to the trap mechanism via a pipe.

Preferably, the heated reaction gas supply mechanism includes a reactiongas heating unit for heating a reaction gas, and the reaction gasheating unit has a heating chamber for heating the reaction gas thereinand a coiled heating element disposed in the heating chamber.

Preferably, a bypass pipe for exhausting the processing gas withoutpassing through the processing chamber is connected to an inlet side ofthe processing chamber.

Preferably, the gas exhaust system further includes a heating/mixingchamber for heating and mixing the processing gas flowing through thebypass pipe and the heated reaction gas supplied from the heatedreaction gas supply mechanism.

In accordance with another aspect of the invention, there is provided afilm-forming apparatus for forming a film on a substrate, including: aprocessing chamber in which a substrate is placed; a processing gassupply mechanism for supplying a processing gas into the processingchamber where the substrate is placed; a unit for causing a film formingreaction on the substrate by imparting energy to the processing gas; anda gas exhaust system for exhausting an exhaust gas in the processingchamber and processing the exhaust gas, wherein the gas exhaust systemincludes: a gas exhaust pipe for exhausting the exhaust gas in theprocessing chamber; a trap mechanism provided to the exhaust pipe, fortrapping a by-product in the exhaust gas; and a heated reaction gassupply mechanism for supplying a heated reaction gas into the exhaustgas, the heated reaction gas adapted to react with a component in theexhaust gas to produce a by-product.

Preferably, the processing gas supply mechanism is provided with a unitfor heating the substrate placed in the processing chamber to form a TiNfilm by causing a film forming reaction on the substrate by supplyingTiCl₄ gas and NH₃ gas as the processing gas into the processing chamber,and NH₄Cl is produced as a by-product by supplying NH₃ gas as the heatedreaction gas from the heated reaction gas supply mechanism.

In accordance with still another aspect of the invention, there isprovided a method for processing an exhaust gas in a film-formingapparatus for forming a film by CVD on a substrate placed in aprocessing chamber by supplying a processing gas into the processingchamber, the method including: exhausting the exhaust gas in theprocessing chamber through a gas exhaust pipe connected to theprocessing chamber; forming a by-product by supplying a heated reactiongas into the exhaust gas flowing in the gas exhaust pipe, the heatedreaction gas adapted to react with a component in the exhaust gas; andtrapping the by-product by a trap mechanism.

Preferably, a TiN film is formed by CVD on a substrate placed in theprocessing chamber by supplying TiCl₄ gas and NH₃ gas as the processinggas into the processing chamber and, at the same time, NH₄Cl is producedas the by-product by supplying NH₃ gas as the heated reaction gas, whichreacts with TiCl₄ in the exhaust gas, into the exhaust gas flowing inthe gas exhaust pipe and, then, the produced NH₄Cl as the by-product istrapped by the trap mechanism.

In accordance with still another aspect of the invention, there isprovided a computer-readable storage medium storing software forexecuting a control program in a computer, wherein, when executed, thecontrol program controls a method for processing an exhaust gas in afilm-forming apparatus for forming a film by CVD on a substrate placedin a processing chamber by supplying a processing gas into theprocessing chamber, the method including: exhausting an exhaust gas inthe processing chamber through a gas exhaust pipe connected to theprocessing chamber; forming a by-product by supplying a heated reactiongas into the exhaust gas flowing in the gas exhaust pipe, the heatedreaction gas adapted to react with a component in the exhaust gas; andtrapping the by-product by a trap mechanism.

In accordance with still another aspect of the invention, there isprovided a computer program for, when executed on a computer,controlling a film-forming apparatus to perform a method for processingan exhaust gas in the film-forming apparatus for forming a film by CVDon a substrate placed in a processing chamber by supplying a processinggas into the processing chamber, the method including: exhausting anexhaust gas in the processing chamber through a gas exhaust pipeconnected to the processing chamber; forming a by-product by supplying aheated reaction gas into the exhaust gas flowing in the gas exhaustpipe, the heated reaction gas adapted to react with a component in theexhaust gas; and trapping the by-product by a trap mechanism.

In accordance with the present invention, by supplying the heatedreaction gas adapted to react with a component in the exhaust gas toproduce a by-product, the reaction for producing a by-product canproceed sufficiently with an increased productivity, so that a stableby-product can be produced to be trapped by the trap mechanism.Accordingly, it is possible to suppress the production of a by-producthaving a highly indefinite element, so that the trap efficiency can beincreased.

Particularly, in case TiCl₄ gas and NH₃ gas are used as the processinggas and NH₃ gas is supplied to the gas exhaust pipe by the heatedreaction gas supply mechanism, a high-density stable NH₄Cl can beproduced as the by-product. This by-product can be easily trapped andthe irregular clogging of the trap mechanism can be reduced. As aconsequence, the by-product can be trapped efficiently without scalingup the trap mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a film-forming apparatus having a gasexhaust system in accordance with an embodiment of the presentinvention;

FIG. 2 shows a schematic view of a heated reaction gas supply mechanismused in the gas exhaust system of the film-forming apparatus shown inFIG. 1;

FIG. 3 provides a partially cutaway perspective view of a trap mechanismused in the gas exhaust system of the film-forming apparatus shown inFIG. 1;

FIG. 4 describes a schematic view of another example of a connection ofa heated reaction gas supply mechanism in the gas exhaust system of thefilm-forming apparatus shown in FIG. 1; and

FIG. 5 offers a schematic view of an example in which a processing gasflowing in a bypass pipe and a heated reaction gas are mixed in aheating/mixing chamber in the exhaust structure of the film-formingapparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENT

Embodiments of the present invention will be described with reference tothe accompanying drawings which form a part hereof. In the presentembodiment, there will be described, as an example, a case where a TiNfilm is formed by CVD on a surface of a semiconductor wafer(hereinafter, referred to as “wafer”) as a substrate to be processed.

FIG. 1 is a schematic view of a film-forming apparatus having a gasexhaust system in accordance with an embodiment of the presentinvention.

A film-forming apparatus 100 includes a film-forming processing unit 200and a gas exhaust system 300.

The film-forming processing unit 200 has a substantially cylindricalchamber (processing chamber) 11 made of aluminum or aluminum alloy(e.g., JIS A5052). In the chamber 11, a susceptor 12 for horizontallysupporting a wafer W as a substrate to be processed is supported by acylindrical supporting member 13 provided at a central bottom portionthereof. A heater 14 is buried in the susceptor 12 to heat the wafer Wto a predetermined temperature.

A shower head 20 serving as a gas injection member is provided at anupper portion of the chamber 11. The shower head 20 is formed in a diskshape and has a gas diffusion space 21 therein and a plurality of gasinjection openings 22 formed at a bottom portion thereof. Moreover, agas supply port 23 is provided at an upper central portion of the showerhead 20.

A circular opening 31 is formed at a central portion of a bottom wall ofthe chamber 11, and a gas exhaust chamber 32 projects downward to coverthe opening 31. A gas exhaust port 33 is formed in a bottom surface ofthe gas exhaust chamber 32. Besides, a loading/unloading port 35 forloading/unloading the wafer W is formed in a sidewall of the chamber 11.The loading/unloading port 35 is openable/closable by a gate valve 36.

A processing gas supply system 40 for supplying a processing gas forfilm formation is connected to the shower head 20 via a pipe 41, and anopening/closing valve 42 is provided in the middle of the pipe 41. Theprocessing gas supply system 40 has a plurality of gas supply sourcesfor supplying TiCl₄ gas, NH₃ gas, N₂ gas and the like, and the gases canbe supplied into the chamber 11 via the pipe 41 and the shower head 20at respective flow rates controlled by a flow rate controller such as amass flow controller. Further, although the pipe 41 is illustrated as asingle pipe for convenience, the gases may be supplied through separatepipes.

Meanwhile, the gas exhaust system 300 has a gas exhaust pipe 51connected to the gas exhaust port 33. As for the gas exhaust pipe 51,there is used one that is made of stainless steel and has an innerdiameter of about 5 to 10 cm. On the gas exhaust pipe 51, there areprovided an opening/closing valve 52, a pressure control valve 53, atrap mechanism 54 for trapping a reaction by-product in an exhaust gas,a vacuum pump 55 for evacuating the chamber 11 and a waste gas scrubber56 for completely removing impurity remaining in the exhaust gas, allbeing disposed in that order from the upstream side. Further, as shownin FIG. 1, the pressure control valve 53 may be provided between thetrap mechanism 54 and the vacuum pump 55 to reduce the reactionby-product adhered to the pressure control valve 53, so that themaintenance cycle of the pressure control valve 53 can be lengthened.

A bypass pipe 58 is connected between an upstream portion of theopening/closing valve 42 in the pipe 41 and a downstream portion of thepressure control valve 53 in the gas exhaust pipe 51. The bypass pipe 58is provided with an opening/closing valve 59. The bypass pipe 58 is usedfor directly exhausting a processing gas supplied to stabilize a gasflow rate to the gas exhaust pipe 51 without passing through the chamber11.

The upstream side of the trap mechanism 54 in the gas exhaust pipe 51 isconnected to a pipe 61 extending from a heated reaction gas supplymechanism 60 via a nozzle 62. The heated reaction gas supply pipe 61 isprovided with a flow rate controller 63 such as a mass flow controllerand an opening/closing valve 64. Further, when the heated reaction gasis supplied from the heated reaction gas supply mechanism 60 to theby-product or the unreacted processing gas flowing in the gas exhaustpipe 51 via the heated reaction gas supply pipe 61 and the nozzle 62, itis possible to produce a stable high-density by-product that is easilytrapped. In the present embodiment, a heated NH₃ gas is typicallysupplied as the heated reaction gas.

As illustrated in FIG. 2, the heated reaction gas supply mechanism 60includes a reaction gas supply source 65 and a reaction gas heating unit66. The reaction gas heating unit 66 has a gas heating vessel 67 forheating a reaction gas and a heating element 68 disposed therein. Theheating element 68 is coiled in a specific shape to have a considerablylarge heating area. The heating element 68 instantly heats the reactiongas supplied to the gas heating vessel 67. A power supply 69 isconnected to the heating element 68, so that the reaction gas is heatedto a desired temperature by controlling the output of the power supply69. At this time, the temperature of the heated reaction gas ispreferably higher than or equal to about 170° C. in view of ensuring thedesired reaction. Further, it is preferably lower than or equal to about400° C. in view of ensuring safety of equipments, and more preferablyabout 200 to 350° C. Further, when the processing gas supply system 40includes the reaction gas, it is possible to omit the reaction gassupply source 65, and the reaction gas can be supplied from theprocessing gas supply system 40.

As depicted in the enlarged view of FIG. 3, the trap mechanism 54 has acylindrical housing 71. Formed at an upper portion of a sidewall of thehousing 71 are an exhaust gas inlet 72 and an exhaust gas outlet 73. Acylindrical cooling chamber 74 is formed on the side of the exhaust gasoutlet 73 of the housing 71 so as to be eccentric with respect to thehousing 71. In the housing 71, the cooling chamber 74 and the outsidethereof communicate with each other at the bottom portion of the housing71. In the outside of the cooling chamber 74 in the housing 71, aplurality of horizontal trap plates 75 having a plurality of gas throughholes 75 a are vertically arranged. Meanwhile, also in the inside of thecooling chamber 74, a plurality of horizontal trap plates 76 having aplurality of gas through holes 76 a are vertically arranged. In thecooling chamber 74, a cooling water pipe 77 is provided to penetrate thetrap plates 76, and the trap plates 76 are cooled by circulating coolingwater in the cooling water pipe 77. Further, a cooling water supply pipe78 a and a cooling water discharge pipe 78 b which are connected to thecooling water pipe 77 are provided outside the housing 71.

In the trap mechanism 54, the exhaust gas introduced through the exhaustgas inlet 72 into the housing 71 flows downward through the gas throughholes 75 a of the trap plates 75 and then reaches the cooling chamber 74at the bottom portion of the housing 71. In the cooling chamber 74, theexhaust gas flows upward through the gas through holes 76 a of thecooled trap plates 76 and is then discharged through the exhaust gasoutlet 73. At this time, the by-product is trapped by the trap plates 75and 76. The trap plates 76 are cooled by the cooling water, so that thetrap efficiency can be increased.

The pipe 41, the bypass pipe 58 and the gas exhaust pipe 51 arerespectively wound by tape heaters 81, 82 and 83, as indicated by dashedlines in the drawings. By heating them to a predetermined temperature,gaseous components are prevented from being condensed inside the pipes.Further, the heated reaction gas supply pipe 61 is wound by a tapeheater 84, so that it is possible to avoid the decreases of thetemperature of the heated reaction gas supplied from the heated reactiongas supply mechanism 60.

Each part of the film-forming apparatus 100 is connected to andcontrolled by a process controller 110 including a micro processor(computer). Further, a user interface 111 is connected to the processcontroller 110. The user interface 111 includes, e.g., a keyboard for aprocess manager to input a command to operate the film-forming apparatus100, a display for showing an operational status of the processcontroller 110 and the like. Moreover, connected to the processcontroller 110 is a storage unit 112 for storing therein, e.g., controlprograms to be used in realizing various processes, which are performedin the film-forming apparatus 100 under the control of the processcontroller 110 and programs, i.e., recipes to be used in operating eachpart of the film-forming apparatus 100 to carry out processes inaccordance with processing conditions. The recipes can be stored in ahard disk or a semiconductor memory, or can be set at a certain positionof the storage unit 112 while being recorded on a portable storagemedium such as a CDROM, a DVD and the like. Further, the recipes can betransmitted from another device via, e.g., a dedicated line. Ifnecessary, the process controller 110 executes a recipe read from thestorage unit 112 in response to instructions from the user interface111, thereby implementing a required process in the film-formingapparatus 100 under the control of the process controller 50.

Hereinafter, a processing operation of the film-forming apparatusconfigured as described above will be described.

First of all, the chamber 11 is evacuated to vacuum by operating the gasexhaust system 300. Next, the wafer W is loaded into the chamber 11 andmounted on the susceptor 12. Thereafter, the wafer W is heated to apredetermined temperature by the heater 14. In that state, TiCl₄ gas,NH₃ gas and N₂ gas are made to flow at respective flow rates from theprocessing gas supply system 40 to the bypass pipe 58, therebyperforming a pre-flow process. After the flow rates of the gases becomestable, the gases are supplied into the chamber 11 via the shower head20 through the pipe 41 and, at the same time, the pressure control valve53 is driven to maintain the inside of the chamber 11 at a predeterminedpressure. In that state, the TiCl₄ gas and the NH₃ gas react on thewafer W maintained at a predetermined temperature on the susceptor 12,thereby depositing a TiN film on the surface of the wafer W.

When the TiN film is formed by supplying the TiCl₄ gas, the NH₃ gas andthe N₂ gas, the exhaust gas is exhausted via the gas exhaust pipe 51. Inthat case, the processing gas consumed by the reaction is only about10%, and most of the processing gas remains unreacted. The unreactedprocessing gas reacts with a reaction gas in the chamber 11 or in thegas exhaust pipe into which the reaction gas is introduced to produce aby-product. The by-product thus produced flows in the gas exhaust pipe51 together with a by-product produced when forming the TiN film.

At this time, if NH₄Cl is mainly produced as the by-product by causingthe reaction of the following Eq. (1) in the chamber 11 and the gasexhaust pipe 51, it can be easily trapped by the trap mechanism 54 inthe form of a stable high-density by-product. In other words, in thepresent embodiment, NH₄Cl is a by-product to be trapped by the trapmechanism 54.

6TiCl₄+32NH₃→6TiN+24NH₄Cl+N₂  Eq. (1)

Meanwhile, when the TiN film is formed, the TiCl₄ gas and the NH₃ gas ofthe processing gas are introduced into the chamber 11 at substantiallythe same flow rates, so that the NH₃ gas is insufficient for causing thereaction of Eq. (1) to occur. Therefore, in the present embodiment, theNH₃ gas is supplimentarily supplied from the heated reaction gas supplymechanism 60 to the pipe 51 in order to cause the reaction of Eq. (1) totake place. At this time, according to Eq. (1), the flow rate of the NH₃gas supplimentarily supplied is preferably four times greater than thatof the NH₃ gas for film formation.

In that case, if the NH₃ gas is introduced at a room temperature, eventhrough the trap efficiency of the trap mechanism 54 increases, thereaction of Eq. (1) proceeds insufficiently, producing a complex(TiCl₄.4NH₃) as an indefinite element obtained by the following Eq. (2).TiCl₄.4NH₃ is difficult to be trapped by the trap mechanism 54, so thatthe trap mechanism 54 needs to be scaled up. Moreover, TiCl₄.4NH₃ has alow density and a high volume. Therefore, if the amount of TiCl₄.4NH₃increases, the trap mechanism 54 may be clogged at an initial stage.Besides, the generation amount of TiCl₄.4NH₃ is not determined, so thatthe trap mechanism is clogged irregularly.

TiCl₄+4NH₃→TiCl₄.4NH₃  Eq. (2)

According to the research on the cause of the above problems, it hasbeen found that when the NH₃ gas is introduced as it is into the gasexhaust pipe 51, the heat energy for the reaction of Eq. (1) isinsufficient. Also, it has been found that the NH₃ gas needs to beheated and supplied to the gas exhaust pipe 51 in order to make thereaction of Eq. (1) predominant while suppressing the reaction of Eq.(2).

In the present embodiment, by introducing the heated NH₃ gas from theheated reaction gas supply mechanism 60 to the gas exhaust pipe 51, theby-product mainly formed of NH₄Cl is produced by the reaction of eq. (1)while suppressing the reaction of eq. (2) and is trapped by the trapmechanism 54. At this time, the temperature of the heated NH₃ gas ispreferably higher than or equal to about 170° C. in view of ensuring thereaction of Eq. (1). Further, it is preferably lower than or equal toabout 400° C. in view of ensuring safety of equipments. When theby-product is trapped by the trap plates 75 and 76 in the trap mechanism54, NH₄Cl is cooled by the trap plates 76 cooled in the cooling chamber74, so that the higher trap efficiency can be maintained.

Here, TiCl₄.4NH₃ is a complex in which four NH₃ molecules arecoordinate-covalent-bonded with a TiCl₄ molecule, and NH₄Cl is anionically bonded salt having a large chemical bonding force. Therefore,if the by-product mainly formed of NH₄Cl is produced by suppressing thegeneration of TiCl₄.4NH₃ as an indefinite element, it is possible toobtain a high-density stable by-product that is easily trapped. Besides,the irregular clogging of the trap mechanism 54 can be reduced. As aconsequence, the by-product can be trapped reliably and efficientlywithout scaling up the trap mechanism 54 and, hence, the maintenancecycle of the trap mechanism can be greatly lengthened. Furthermore, incase the average maintenance cycle is made to be equal to that of aconventional trap mechanism, the trap mechanism 54 can become compact insize.

In addition, according to a result of a test performed by using theconventional trap mechanism as the trap mechanism 54, it has been foundthat the volume of the by-product can be reduced to about ⅓ and alsothat the maintenance cycle of the trap mechanism 54 can be lengthened bythree times.

The exhaust gas remaining after the by-product is trapped by the trapmechanism 54 is led to the waste gas scrubber 56 via the vacuum pump 55,and impurity components are completely removed therein. As the reactionproceeds according to Eq. (1), TiN as well as NH₄Cl can be trapped bythe trap mechanism 54. Further, since N₂ is a harmless gas component,the amount of harmful impurity components that are not trapped by thetrap mechanism 54 can be minimized and, hence, the burden on the wastegas scrubber 56 can be reduced. As a result, the running cost of thewaste gas scrubber 56 can be reduced, and the lifespan thereof can beextended.

Since the heated NH₃ gas supplied from the heated reaction gas supplymechanism 60 is supplied via the pipe 61, the temperature thereof maydecrease when it reaches the gas exhaust pipe 51. However, the NH₃ gascan be supplied at a desired temperature by heating the pipe 61 with thetape heater 84 to suppress the temperature decrease thereof.

In the present embodiment, the heated NH₃ gas is introduced into the gasexhaust pipe 51 and, thus, the reactivity increases. As a consequence,when the heated NH₃ gas is supplied to the gas exhaust pipe 51, it isonly required to connect the nozzle 62 to the gas exhaust pipe 51.Moreover, due to the high reactivity, the heated NH₃ gas may be directlyintroduced into the trap mechanism 54 by providing a gas inlet port 79at the trap mechanism 54 and connecting the pipe 61 thereto, asillustrated in FIG. 4.

Moreover, instead of directly connecting the bypass pipe 58 to the gasexhaust pipe 51, it is possible to provide a heating/mixing chamber 85in the middle of the pipe 61 and connect the bypass pipe 58 thereto, ascan be seen from FIG. 5. Accordingly, the processing gas flowing fromthe bypass pipe 58 can be made to flow into the gas exhaust pipe 51,after being heated and mixed with the heated NH₃ gas. As a result, thetrap efficiency of the processing gas flowing through the bypass pipe 58can be further increased.

The present invention can be variously modified without being limited tothe above embodiments. For example, in the above embodiments, there hasbeen described an example in which a TiN film is formed by using TiCl₄gas and NH₃ gas. However, the present invention can be applied tovarious film forming processes to be described below, without beinglimited to the above example.

(1) When the present invention is applied to the case of forming a Tifilm by using TiCl₄ gas and H₂ gas, HCl is a by-product to be trapped.By supplying a heated H₂ gas as a heated reaction gas into the exhaustgas, HCl can be trapped stably.

(2) When the present invention is applied to the case of forming a Wfilm by using WF₆ gas and SiH₄ gas, SiF₄ and HF are by-products to betrapped. By supplying a heated SiH₄ gas as a heated reaction gas intothe exhaust gas, SiF₄ and HF can be trapped stably.

(3) When the present invention is applied to the case of forming a Wfilm by using WF₆ gas and SiH₂Cl₂ gas, SiF₄, HF, HCl and Cl₂ areby-products to be trapped. By supplying a heated SiH₂Cl₂ gas as a heatedreaction gas into the exhaust gas, SiF₄, HF, HCl and Cl₂ can be trappedstably.

(4) When the present invention is applied to the case of forming a Ta₂O₅film as a high-k dielectric film by using Ta(OC₂H₅) gas, a high-densitysolid having an indefinite composition can be stably trapped bysupplying heated steam or heated O₂ gas as a heated reaction gas intothe exhaust gas.

Further, in the above embodiments, there has been described an examplein which NH₃ gas as a reaction gas is heated while passing through theheating element 68 that is coiled in a specific shape in the gas heatingchamber 67 to have a considerably large heating area. However, theconventionally known gas heating unit can be widely used without beinglimited to the above example.

In addition, the structure of the trap mechanism 54 is not particularlylimited, and a trap mechanism having a conventional structure can beemployed.

Furthermore, in the above embodiment, a semiconductor wafer is used asan example of a substrate to be processed. However, it is not limitedthereto, and there may be used another substrate such as a glasssubstrate for a flat panel display (FPD) represented by a liquid crystaldisplay (LCD).

1. A gas exhaust system of a film-forming apparatus for forming a filmby CVD on a substrate placed in a processing chamber by supplying aprocessing gas into the processing chamber, the gas exhaust system ofthe film-forming apparatus comprising: a gas exhaust pipe connected tothe processing chamber, for exhausting an exhaust gas in the processingchamber; a trap mechanism provided to the gas exhaust pipe, for trappinga by-product in the exhaust gas; and a heated reaction gas supplymechanism for supplying a heated reaction gas into the exhaust gas, theheated reaction gas adapted to react with a component in the exhaust gasto produce a by-product.
 2. The gas exhaust system of claim 1, wherein aTiN film is formed by CVD on the substrate placed in the processingchamber by supplying TiCl₄ gas and NH₃ gas as the processing gas intothe processing chamber and, at the same time, NH₄Cl is produced as aby-product by supplying NH₃ gas as the heated reaction gas from theheated reaction gas supply mechanism.
 3. The gas exhaust system of claim2, wherein the NH₃ gas as the heated reaction gas is supplied whilebeing heated at about 170° C. or higher.
 4. The gas exhaust system ofclaim 1, wherein the heated reaction gas supply mechanism supplies theheated reaction gas to an upstream side of the trap mechanism on the gasexhaust pipe via a pipe.
 5. The gas exhaust system of claim 1, whereinthe heated reaction gas supply mechanism supplies the heated reactiongas to the trap mechanism via a pipe.
 6. The gas exhaust system of claim1, wherein the heated reaction gas supply mechanism includes a reactiongas heating unit for heating a reaction gas, and the reaction gasheating unit has a heating chamber for heating the reaction gas thereinand a coiled heating element disposed in the heating chamber.
 7. The gasexhaust system of claim 1, wherein a bypass pipe for exhausting theprocessing gas without passing through the processing chamber isconnected to an inlet side of the processing chamber.
 8. The gas exhaustsystem of claim 7, further comprising a heating/mixing chamber forheating and mixing the processing gas flowing through the bypass pipeand the heated reaction gas supplied from the heated reaction gas supplymechanism.
 9. A film-forming apparatus for forming a film on asubstrate, comprising: a processing chamber in which a substrate isplaced; a processing gas supply mechanism for supplying a processing gasinto the processing chamber where the substrate is placed; a unit forcausing a film forming reaction on the substrate by imparting energy tothe processing gas; and a gas exhaust system for exhausting an exhaustgas in the processing chamber and processing the exhaust gas, whereinthe gas exhaust system includes: a gas exhaust pipe for exhausting theexhaust gas in the processing chamber; a trap mechanism provided to theexhaust pipe, for trapping a by-product in the exhaust gas; and a heatedreaction gas supply mechanism for supplying a heated reaction gas intothe exhaust gas, the heated reaction gas adapted to react with acomponent in the exhaust gas to produce a by-product.
 10. Thefilm-forming apparatus of claim 9, wherein the processing gas supplymechanism is provided with a unit for heating the substrate placed inthe processing chamber to form a TiN film by causing a film formingreaction on the substrate by supplying TiCl₄ gas and NH₃ gas as theprocessing gas into the processing chamber, and NH₄Cl is produced as aby-product by supplying NH₃ gas as the heated reaction gas from theheated reaction gas supply mechanism.
 11. A method for processing anexhaust gas in a film-forming apparatus for forming a film by CVD on asubstrate placed in a processing chamber by supplying a processing gasinto the processing chamber, the method comprising: exhausting theexhaust gas in the processing chamber through a gas exhaust pipeconnected to the processing chamber; forming a by-product by supplying aheated reaction gas into the exhaust gas flowing in the gas exhaustpipe, the heated reaction gas adapted to react with a component in theexhaust gas; and trapping the by-product by a trap mechanism.
 12. Themethod of claim 11, wherein a TiN film is formed by CVD on a substrateplaced in the processing chamber by supplying TiCl₄ gas and NH₃ gas asthe processing gas into the processing chamber and, at the same time,NH₄Cl is produced as the by-product by supplying NH₃ gas as the heatedreaction gas, which reacts with TiCl₄ in the exhaust gas, into theexhaust gas flowing in the gas exhaust pipe and, then, the producedNH₄Cl as the by-product is trapped by the trap mechanism.
 13. Acomputer-readable storage medium storing software for executing acontrol program in a computer, wherein, when executed, the controlprogram controls a method for processing an exhaust gas in afilm-forming apparatus for forming a film by CVD on a substrate placedin a processing chamber by supplying a processing gas into theprocessing chamber, the method comprising: exhausting an exhaust gas inthe processing chamber through a gas exhaust pipe connected to theprocessing chamber; forming a by-product by supplying a heated reactiongas into the exhaust gas flowing in the gas exhaust pipe, the heatedreaction gas adapted to react with a component in the exhaust gas; andtrapping the by-product by a trap mechanism.
 14. A computer program for,when executed on a computer, controlling a film-forming apparatus toperform a method for processing an exhaust gas in the film-formingapparatus for forming a film by CVD on a substrate placed in aprocessing chamber by supplying a processing gas into the processingchamber, the method comprising: exhausting an exhaust gas in theprocessing chamber through a gas exhaust pipe connected to theprocessing chamber; forming a by-product by supplying a heated reactiongas into the exhaust gas flowing in the gas exhaust pipe, the heatedreaction gas adapted to react with a component in the exhaust gas; andtrapping the by-product by a trap mechanism.